1. Field of the Invention
The present invention relates to a recoil starter having a recoil rope wound around a rope reel, wherein one end of the recoil rope drawn outside a casing of the recoil starter is pulled to rotate the rope reel so that a rotational force of the rope reel is transmitted to a cam via a damper spring, and then a rotation of the cam is transmitted to a rotational member coupled to a crankshaft of an engine via a ratchet mechanism to rotate the rotational member, whereby the engine is started.
2. Description of the Related Art
Among recoil starters designed to transmit a rotation of a rope reel, rotated by pulling a recoil rope, to a cam and further rotate a rotational member such as flywheel magnet or drive pulley via a centrifugal clutch or other ratchet mechanism which engages with or disengages from the cam, a recoil starter has been proposed which is constructed to absorb a shock, caused due to fluctuations in load during engine startup and transmitted to an operator's hand, by resiliently coupling the rope reel and the cam through a damper spring in the form of a coil spring to transmit a rotation of the rope reel to the cam via the damper spring.
In the proposed recoil starter, as shown in FIG. 8, a damper spring 34 is received within annular recesses 32 and 33 which are formed on opposing surfaces of a rope reel 30 and a cam 31 while one end portion 35 thereof bent in U shape is fitted within a holding groove 36 formed on the rope reel 30 and the other end portion 37 thereof, bent in an axial direction, is inserted into an opening 38 formed in the cam 31, so that the rope reel 30 and the cam 31 are rotationally coupled to each other via the damper spring 34. When a rope 39 wound around the rope reel 30 is pulled to rotate the rope reel 30, the cam 31 is rotated via the damper spring 34. As a result, engagement of cam pawls 40 formed on the outer peripheral surface of the cam 31 with a ratchet 42 provided on a rotational member 41 attached to a crankshaft of an engine allows a rotation of the cam 31 to be transmitted to the rotational member 41, whereby the crankshaft coupled to the rotational member 41 is rotated. When the rotation of the cam 31 is precluded by a startup resistance of the engine, the damper spring 34 is twisted, so that a shock on the rope reel 30 is cushioned and a rotational force of the rope reel 30 is stored in the damper spring 34. When a driving force of the rope reel 30 exceeds the startup resistance of the engine, the rotational force stored in the damper spring 34 is released, so that the rotational member 41 is rotated via the cam 31 to start the engine (e.g., Japanese Patent Application No. 2002-144695).
In the proposed recoil starter, the opposite end portions 35 and 37 of the damper spring 34 are held on the rope reel 30 and the cam 31 in a fixed manner, respectively. Thus, the end portions 35 and 37 of the damper spring 34 cannot radially move. Therefore, although a middle part of a coiled portion of the damper spring 34 winds and tightens around the outer peripheral surfaces of bosses 43 and 44 of the rope reel 30 and the cam 31, opposite ends of the coiled portion are deformed to the extent that the ends are detached from the outer peripheral surfaces of the bosses 43 and 44 as shown in FIG. 8. Under such a condition, the bent portions at the opposite ends of the damper spring 34 undergo an excessive stress, possibly resulting in breakage of the damper spring 34.
A technique has been proposed which restricts the relative rotational angle between the rope reel 30 and the cam 31 by stopper means arranged between the rope reel 30 and the cam 31 to keep load on the damper spring 34 below a predetermined setting. In this technique, however, when the stopper means operates, a feel of collision is caused and transmitted as a shock to the operator's hand pulling the recoil rope 39, resulting in an unpleasant feel during startup. Further, since the cam 31 is simply supported at its central portion by a shaft 46 formed on a casing 45 so as to be rotatable, when a spring force of the damper spring 34 acts on the cam 31 while only one of the ratchets 42 is engaged with the cam pawl 40, an eccentric load or a strong leaning force acts on the cam 31, possibly resulting in breakage of the cam 31.
Further, it is desirable that the damper spring 34 have greater shock-absorbing and force-storing capabilities. While these capabilities can be enhanced by increasing a wire diameter and a winding diameter of the damper spring 34, the sizes of the annular recesses 32 and 33 receiving the damper spring 34 must be increased in outer diameter thereof corresponding to the increase of the wire diameter and winding diameter of the damper spring 34. In the proposed technique, the cam pawls 40 are formed such that the cam pawls 40 protrude outwardly from the outer surface of an outer peripheral wall 47 of the annular recess 33 formed on the cam 31 to receive therein the damper spring 34, as shown in FIGS. 9A and 9B. Therefore, the outer size of the cam 31 is restricted in relation to such parts as the ratchet 42, a cooling fan formed on the rotational member 41, the casing 45 and the like. Consequently, since the size of the annular recess 33 is thus restricted, it is difficult to increase the wire diameter and winding diameter of the damper spring 34 unless the overall size of the recoil starter is scaled up.